A radio frequency identification (RFID) technology is known in which an RFID reader/writer reads information from an RFID tag by a short-distance wireless communication via radio waves or an electromagnetic field. This RFID technology is widely used in tickets for trains, busses, etc., digital money, staff identity cards, etc.
Techniques of using the RFID technology for position measurement are also known. For example, a configuration is known which shoots a subject with a video camera while its three or more wireless communication units communicate with a wireless tag attached to the subject and measures the position of the subject on the principle of trilateration using differences between times that wireless signals take to travel from the wireless tag to the respective wireless communication units (see JP-A-2008-227877, for instance). Information of the measured position of the subject is displayed on a display unit of the video camera.
There is a demand for application of the RFID technology to management of goods such as goods stored in a warehouse. More specifically, goods in stock are managed in such a manner that users read, with an RFID reader/writer, RFID tags attached to reading subject goods in a warehouse. Since the RFID tag readable range is small, it is necessary for a user to move to find a reading subject article to which an RFID tag is attached. However, there may occur an event that a user who is not experienced in good management work does not know an approximate position of an article and hence needs to search for it. This may be a heavy work load and take long time.
The related-art configuration which measures the position of a subject to which a wireless tag is attached through trilateration allows a user to measure the position of a subject by approaching it if an approximate position of the subject (wireless tag) is known. However, in a state that the position of a subject is not known at all, a user is required to find the subject and approach it. As a result, even if the conventional trilateration-based position measurement technology using a wireless tag is applied to goods management, users may suffer heavy work loads and long work hours.